1. Field of the Invention
The present invention relates to an ethylene-based polymer comprising ethylene and a vinyl compound having a substituent having specific steric parameter, an ethylene-based polymer having excellent mechanical strength property, and an ethylene-based polymer having excellent processing property and mechanical strength property, a method for producing the ethylene-based polymer, and a use thereof.
2. Description of the Related Art
Ethylene-based polymers are widely used in various fields as general resins, and required to have mechanical properties such as rigidity, impact strength and the like, for example, and excellent appearance such as transparency and the like, in addition to molding processability. Regarding a conventional linear low density polyethylene prepared by using butene-1 or hexene-1 as a copolymerization component for ethylene, increase in molecular weight and decrease in density for improving mechanical properties are proposed, however, these means are not admitted as appropriate methods since deterioration in processability due to increase in extrusion tolque in processing and decrease in heat-resistance are occurred, and there is limitation to improvement in mechanical properties.
As an ethylene-based copolymer having specific viscoelastic property, an ethylene-based copolymer prepared by using styrene or 4-vinylcyclohexene as a copolymerization component for ethylene is disclosed (Japanese Patent Application Laid-Open (JP-A) No. 7-70223). However, an ethylene-styrene copolymer is not preferable since it causes decrease in impact strength and deterioration in transparency due to inclusion of a polystyrene by-produced in production. Further, an ethylene-vinyl cyclohexene copolymer exhibits poor heat stability since it contains a double bond in a significant amount derived from 4-vinylcyclohexene, and includes problems such as occurring of fish eye due to gelling in molding process and the like.
On the other hand, an ethylene-based copolymer using vinylcyclohexane as a copolymerization component for ethylene is reported (Polymer Science (1991), vol. 33(11), p. 2318). However, it is not admitted to have excellent mechanical strength and transparency since it has wide composition distribution due to production in the presence of a Ziegler Natta catalyst system. There is also a report of production in the presence of a metallocene catalyst system (Polymer (1993), vol. 34(9), 1941/Polymer Science USSR (1990), vol. 32(9), 1868), however, it has extremely low molecular weight and therefore the mechanical strength can not be admitted as in satisfactory level.